Aluminum-magnesium casting alloys



Aug C. B. WILLMORE ALUMINUM-MAGNESIUM CASTING ALLOYS 2 Sheets-Sheet 1 Filed Jan. 14, 1949 Q91 GRAPH I, SHOWING EFFECT OF BORON AND BERYLLIUM AS'INTENSIFIER FOR THE GRAIN REFINING OF TITANIUM IN AL-MAG ALLOYS HAVING 6.5 PERCENT MAGNESIUM I -II I.OO

s A ee T BB M i. w w W BMTT TT I N%%// T 0000 m m odmmmz D A ABCDEFG D O a G M 0 0 3 O .0. o 2 r O 5 O D E f: l C a O O u O O o O O o w m w. 2 I. o. O O O O O O O PERCENT BORON /N ALLOY ATTORNEYS. l

C. B. WILL Aug. 14, 1951 MORE ALUMINUM-MAGNESIUM CASTING ALLOYS 2 Sheets-Sheet 2 Filed Jan. 14, 1949 GRAPH SHOWING EFFECT OF TITANIUM I ON THE PHYSICAL PROPERTIES OF ALUM|NUM .Ol Be ALI OYED WITH 6.5 MAGNESIUM.

w E 8 4 O TITAN/UM IN PERCENT g WzjNVENTOR: 5r M,%%&% QWI Patented Aug. 14, 1951 2,564,044 ALUMINUM-MAGNESIUM CASTING ALLOYS Charles B. Willmore, North Aurora, 111., assignor to William F. Jobbins, Inc., Aurora, 111., a corporation of Illinois Application January 14, 1949, Serial No. 71,015;

-9 Claims.

This invention relates to aluminum alloys constituted with magnesium as the major alloying element, and, more particularly, it relates to new and improved aluminum-magnesium alloys for fabrication into finished products by the casting technique.

Commercially, aluminum-magnesium casting alloys may be arranged into two distinct groups. Cast alloys having a magnesium content ranging from 9 to 12 percent by weight are responsive to heat treatment by which their physical properties are greatly improved. In this treatment, the aluminum-magnesium intermetallic compounds are put into solid solution from which they are reprecipitated at room temperature in finely divi'ded form instead of the coarse crystals in which they existed in the original casting. The major portion of reprecipitation takes place within a few days :of aging whereby improved physical properties are developed.

In the range of 3 to 9 percent magnesium, heat treatment has very little effect on the physical properties developed on casting. Alloys within this lower group form the subject matter of this invention. Their physical properties developed on casting are generally referred to as the as cast properties. Within this group, further subdivision is possible with respect to the method of casting; that is, casting may be made into sand molds, hereinafter referred to as sand casting, or'it may be made into permanent molds, hereinafter referred to as chill casting. Permanent mold or chill casting may rely entirely on gravitationalprinciples, or the use of positive pressure may be employed in filling the molds, as in die casting. A chief difference between the two types of casting resides in the rate of heat transfer through the mold walls, it being greater in chill casting with the result that crystallization and solidification are more rapid.

Chill casting usually has the effect of decreasing grain size of the cast alloys, especially when they are composed of an aluminum base. In aluminum-magnesium alloys, components, such as magnesium, present in quantities above their normal solid solubility limit at room temperature are retained in meta-stable condition of solid solution instead of precipitating out as in the slower cooling sand casting methods. Ordinarily, these characteristics in --a metal or alloy lead to improved physical properties, but the reverse effects are obtained with aluminummagnesium alloys. There is no satisfactory explanation for the distinguishing deficiency in behavior of aluminum-magnesium alloys to de 2" velop superior properties responsive to finer grain size and increased amount of magnesium in solid solution. No one, to my knowledge, has been able to manufacture an aluminum-magnesium alloy for chill casting which has physical properties that are as high or higher than those obtained by casting the same alloy in sand.

It is an object of this invention to produce an aluminum-magnesium alloy which is not subject to the limitations of the prior art in that it can be used for both chill and sand casting without substantial difference in physical properties.

Another object is to produce an aluminummagnesium alloy for casting into sand, refractory, or metal molds to provide a cast product having improved physical properties without theneed for any heat treatment.

A further object is to produce an aluminummagnesium casting alloy that has properties superior to any heretofore obtained by either sand casting or by heat treatment; that has excellent tensile strength and ductility without heat, treatment; that is as resistant to corrosion as most of the aluminum-magnesium alloys, alloys which are distinguished by their excellent corrosion resistance and high luster; that has optimum machining properties; that acquires and retains a brilliant surface responsive to simple polishing; and that developes high mechanical properties immediately upon cooling to room temperature, which properties do not change with age as compared with heat treated castingswhich develop equivalent tensile strength with age but with a corresponding loss in elongation or ductility such that the product ultimately might become embrittled.

A still further object is to produce an alumnium-magnesium alloy which is particularly adapted to develop superior physical properties by chill casting although it may be successfully sand cast.

A still further object is to produce an aluminum alloy constituted with 3 to 9 percent magnesium as the major alloying element and with other metals in .various new arrangements to provide for specific improvements in the physical characteristics of the cast alloy whereby excellent combinations of tensile strength, yield strength, and elongation are developed without resorting to expensive heat treatment, which is also a deterrent to the rate of production. V

A further object is to produce an aluminummagnesium alloy which embodies alloying principles differing from those heretofore followed to provide for improved characteristics in th alloy.

Briefly described, invention resides in alloying with aluminum and magnesium, minor but important quantities of titanium, beryllium, boron, and manganese or chromium to form new and improved quaternary systems, five-component systems, and six-component systems by the incorporation of selected metals to provide alloys having improved characteristics differing from those heretofore produced not only in composi tion but because of alloying principles heretofore unrecognized in the production of new and improved products. As previously pointed out, this invention is directed primarily to aluminummagnesium alloys for use in as cast condition and, therefore, is limited to less than 9 percent magnesium content, it being understood that best properties are developed with magnesium present in the range of 6 to 8.5 percent. Heretofore, the best aluminum alloy, having 6 to 8.5 percent magnesium, gave a tensile strength of 32,000 pounds per square inch and elongation in the order of 10 percent; whereas, by practicing my invention, an aluminum-magnesium alloy may be produced having as cast properties which measure 42,000 pounds per square inch tensile and percent or more elongation, a combination of properties which exceeds that obtainable with heat treated cast aluminum alloys of the same aluminum content and is comparable in many instances to alloys with higher magnesium content.

To develop improved physical properties in metal alloys, effort is made to reduce the grain size by means which are not deleterious to others of the more important physical characteristics. Boron, as well as titanium, molybdenum, and vanadium, has the reputation of grain refining aluminum base alloys, but this reputation is redicated primarily on its effect with aluminum alloyed with copperand the like. By itself, boron is not a grain refiner in aluminum-magnesium alloys. This can best be illustrated with reference to chart I showing that by the addition of 0.001 percent boron, the grain diameter of the resulting aluminum-magnesium alloy is increased from 0.59 to 0.99 millimeter in diameter, and by the addition of 0.005 percent boron, the grain diameter is increased still further to 1.00 millimeter.

I have found that boron, which is not a grain refiner when added by itself to aluminum-magnesium alloys, nevertheless, acts as desired on an aluminum-magnesium alloy, which has been grain refined as far as possible with titanium, to refine the grain still further provided that beryl-. lium is also present; that is, boron and beryllium serve to intensify the grain refining effect of titanium although neither boron nor beryllium alone has this intensifying effect on titanium. This is also illustrated by chart I drawn from the results secured from a large number of experiments. In the chart, lines B and D indicate that the grain size increases with the addition of boron to an alloy in which either beryllium or titanium alone is present. On the other hand, lines E, F, and G show that the grain size decreases from a relatively low value as the amount of boron is increased when in the presence of both titanium and beryllium in the aluminummagnesium alloy.

In formulating with boron to secure the desired results, I prefer to limit the use of boron to less. than 0.01 percent by weight because it appears that aluminum magnesium alloys are'in- 4 capable of retaining more in solution and that excess boron is precipitated out as an intermetallic compound of boron, which does not appear to add to the physical properties of the alloy but instead becomes detrimental, especially if the amount of precipitation is excessive. For sand casting, it is best to hold the beryllium content to less than 0.03 percent by weight but, preferably, in the range of 0.005 to 0.02 percent. For chill casting, beryllium content as high as 0.20 is useful, but it is most economical to hold the beryllium content to lessthan 0.07 percent. In any event, more than 0.001 percent beryllium should be used.

It appears that maximum benefit of titanium is derived when it is present in amounts ranging-from 0.01 to 0.2- percent. Larger quantities, up to, at least 0.40 percent titanium, may be used; however, it is probable that amounts in excess of 0.25 percent do not remain dissolved in the alloy throughout its freezing range and, therefore, can be of little additional benefit. Furthermore, it appears that as the liquid alloy passes through its freezing range, the excess titanium tends to form precipitates of intermetallic compounds with other metals, making the liquid metal more sluggish to the extent that excess titanium may be detrimental to the mechanical properties of the casting. In view of the above, I prefer to use less than 0.25 percent titanium, with best results being secured with amounts ranging from 0.10 to 0.25 percent titanium.

Grain size is an important factor in the de-' termination of the physical characteristics of an aluminum-magnesium alloy. Grain refinement leads to improvement in tensile strength, yield strength, and elongation or ductility, properties which spell the acceptability and commercial success of the alloy in various applications. Grain refinement, therefore, is an important characteristic and the discovery of means whereby it may be effected to control-or improve other physical properties constitutes an important advance in metallurgical compositions, and the means by which it is secured suggests new alloying principles. This I have accomplished with a new and improved five-component system of aluminummagnesium, boron, titanium, beryllium within the limitations described.

Invention also resides in the use of titanium in such quantities as unexpectedly and more effectively to counteract the coarsening of the grain size occasioned by the addition of beryllium to aluminum-magnesium alloys for the purpose of increasing resistance of th molten alloy to atmospheric attack. It is known that atmospheric attack can be lessened by the presence of I beryllium, but with the sacrifice of grain size and, therefore, other important physical properties of the alloy.

In the past, titanium has been added in amounts ranging up to 0.05 percent to neutralize the negative grain coarsening effect of beryllium, the result being the algebraic balance between the coarsening effect of beryllium and the refining effect of titanium. However, the art has failed to appreciate advantages which might be secured by the addition of more than 0.10 percent titanium. It has been apparent that grain refinement with titanium reaches a maximum at about 0.10 percent and the art has been of the opinion that further additions would be valueless.

I have found that there is a critical range beyond the 0.10 percent titanium wherein further it tends to fall off again at increased amounts up f 5 unexpected improvements are secured in an aluminum-magnesium-beryllium alloy. The fact that titanium beyond 0.10 percent gives further physical improvement without further grain refinement is explainable on the basis that titanium in the higher ranges acts as an alloying constituent. This fact was not predictable because titanium is ordinarily regarded as a grain refiner only, and the fact that larger amounts beyond the limit for grain refinement will thus take on this added function of physical improvement is a matter that was heretofore unknown.

This new relationship is illustrated in chart I! wherein yield strength, tensile strength, and elongation are increased by the addition of titanium to an aluminum-magnesium alloy constituted with beryllium. The increase in physical properties is of a desired order when titanium is incorporated in amounts up to 0.05 percent, but

to 0.10'percent. It is, perhaps, this latter trend which has discouraged investigation of further amounts. I have found, as illustrated by the chart, that further additions of titanium up to 0.20 or perhaps 0.25percent give disproportionate results increasing the strength properties to a very desirable degree, whereby the alloy attains strength characteristics. heretofore unobtainable in as cast condition.

- The ultimate strength of 39,000 pounds per square inch together with 15.3 per-cent elongation represents a most unusual combination'of high strength and high elongation, the previous maximum for a 6.5 percent magnesium alloy being in the range of 32,000-pounds per square inch strength and 10 percent elongation. This improvement alone constitutes a valuable advance in the metallurgy of aluminum-magnesiu alloys. From a practical standpoint, the amount i strength and hardness does not hold true for aluminum-magnesium alloys and especially for aluminum-magnesium titanium-beryllium alloys of the type which constitute the basis of my invention herein embodied. For example, it has been suggested that copper, iron, silicon, zinc, or zirconium have the properties of increasing hardness and strength of aluminum and its alloys; yet, I have found that these same metals when used in quantities which might be expected to improve the yield strength, are excessively detrimental to the properties of the aluminum-magnesium-beryllium-titanium alloys.

Of the metals alloyed with aluminum, magnesium, beryllium, and titanium, manganese and boron each has the desired effect of increasing yield strength beyond the ordinary value of 17,000 pounds per square inch but this is accomplishedwith some loss of ductility and ultimate strength. This more or less follows the accepted theory that elongation is sacrificed for yield strength secured in increasing values by alloying, by mechanical working, by heat treating, or by aging and the like. Most interesting, therefore, is the phenomenon wherein, by the addition of both manganese and boron, together to the alloy containing aluminum, magnesium, beryllium, and titanium, not only is the yield strength increased but the increase is secured without noticeable sacrifice of elongation and withthe further increase of ultimate strength. By the use of this newly discovered alloying principle, I have been able to produce aluminummagnesium alloys having physical properties which are far beyond those heretofore obtain for cast alloys.

Table I illustrates the concept wherein an alloy constituted with both boron and maganese provides for physical properties far superior to those 40 secured with the addition of either manganese or of beryllium which may be incorporated correboron alone or without any addition.

Table No. I

Percentage 1 a Ultimate Y1eld Strength, Strength, g b f f Mg Be Ti Mn B Lbs/Sq. In. Lbs/Sq. In.

6. 5 0. 01 0. 20 none none balance 39, 000 17, 400 15. 3 6. 6 0. 01 0. 20 0. 20 none balance 38, 700 19, 300 10. 7 0.5 0. 01 0.20 none, 0. 00s balance as, 000 17,700 13.7 6.6 0.01 0. 20 1 0 20 0. 004 balance 41,200 19,500 15.1

sponds to the ranges previously pointed out for reaction with boron and beryllium to intensify the grainrefinement of titanium. Titanium in;;5 amounts up to 0.40 percent may be used, but I" prefer to hold the titanium content to less than 0.25 and more specifically to between 0.10 and 0.25 percent.

To the present, description is confined to the.;., concepts and compositions wherein new and improved metallurgical principles are employed to secure high strength and high elongation or ductility in an aluminum-magnesium alloy which also may be constituted with beryllium to'retain- 5 advantage of its stabilizing characteristics with respect to atmospheric attack and the reduction of dross formation in the molten alloy. Important is the need for high yield strength in an aluminum-magnesium alloy without the sacrifice of the physical properties already achieved. As previously pointed out, I have found that known metallurgical data with respect to the effects of additions of other metals to aluminum alloys for the purpose f.securing-improved It will be apparent from the table that the addition of 0.20 percent manganese causes a very desirable increase in yield strength but with about 33 percent loss in elongation and some slight loss .in ultimate strength; that the addition of 0.003' percent boron increases the yield strength to a lesser degree but with a proportional loss in elongation; that the addition of both boron and manganese gives yield in ultimate strength-figures which are higher than those secured by either metal alone and without significant loss in elongation.

For reasons previously indicated, I prefer-to hold the boron content to more than 0.001 percent and less than 0.01 percent to secure maximum benefit thereof in alloys of the type embodied in my invention. I have found that the desired results of good yield strength, elongation, and tensile strength are secured when the amount of manganese is above 0.001 percent but, preferably, within the range of 0.15 to 0.30 percent by weight for sandcasting while 0.20 to 0.60 percent may beused for chill casting alloys Greater yield strength can be secured with increased amounts of manganese but, under such circumstances, there often is some sacrifice of elongation. In any event, up to 1.5 percent manganese may be used in special applications where it is desired to develop maximum yield strength. For example, unusually high yield strengths of 24,000 pounds per square inch may be secured by the addition of 1.2 percent manganese.

Though not equivalent in the sense that one metal can be substituted partially for the other, chromium may be used instead of manganese to achieve the desired results. Chromium, used to best advantage in chill casting and in the absence of manganese, is efiective in concentrations of 0.1 5 to 0.50 percent by weight.

From a practical standpoint, the six-component system constituting the principal features of my invention has the added advantage that the defined characteristics apply to both sand casting and chill casting. This is unusual in aluminummagnesium alloys because of the vast differences that exist in their crystallization whereby finer grain size and the retention of excess metals as solid solutions are characteristic of chill casting. For most aluminum alloys, physical properties developed by chill casting are superior to those obtained by sand casting, but for aluminum-magnesium alloys, the reverse is more often true. This is best illustrated by Table II which shows the physical properties determined after sand and chill casting. To the best of my knowledge, no one heretofore has developed an aluminum-magnesium alloy which gives physical properties by chill casting which are comparable to the same By the slight variations of percentages of these same elements within the limitations prescribed, it is possible to achieve an alloy wherein the properties developed by chill casting, especially in molds heated to GOO-900 F., are even higher in many respects than those secured by the best sand cast alloys. In many instances, the same alloy may be used for sand casting and for chill casting interchangeably and still develop excellent physical properties. A common formulation for use in such two dissimilar casting processes is an'achievement which has been the subject of concentrated research.

For chill casting, the boron content should be less than 0.01 percent but more than 0.001 percent to be effective. Beryllium, in amounts up to 0.05 percent, is very effective, and excellent physical properties have been developed with as much as 0.2 percent, but because of its high cost, use beyond 0.07 percent may not be economical. Reasons previously pointed out for keeping the titanium content below 0.40 percent and, preferably, below 0.25 but above 0.10 percent still hold true. Maximum tensile strength is developed with the presence of 0.20-0.60 percent manganese,

especially when the alloy contains up to 0.20 percent beryllium. However, up to 1.5 percent manganese may be used to secure maximum yield strength.

In production the alloy may be compounded by the addition of the metallic component to molten aluminum maintained at least degrees above melting temperature. To the molten aluminum, the other elements may be added in any desirable order, conforming to accepted metallurgical practices limited to the production of an end product having the elements present in desired amounts and free of harmful impurities. In some instances, it is better to alloy with pure metals, while in other instances, additions may best be made as master alloys or as inorganic salts from which the metal may be made available and from which benefit may be had of certain released gases and compositions which tend to remove impurities and gases from the melt. For example, beryllium may be incorporated as a master alloy with aluminum, and titanium and boron may be added to advantage as inorganic salts.

By way of illustration but not by way of limitation, my invention may be described as being embodied in an aluminum-magnesium alloy constituted with the following.

Per cent Magnesium 1.0-9.0 Titanium 0.001-0.40 Manganese 0.001-1.50 Beryllium 0.001-0.2 Boron 0.001-0.01 Aluminum plus impurities balance For sand casting, best results are secured when the materials are present in the following ratio:

Per cent Magnesium 6.0-7.5 Titanium 0.10-0.25 Manganese 0.15-0.30 Beryllium 0.001-0.03 Boron 0.001-0.01 Aluminum plus impurities balance Slight variations in amounts are required to secure best results for chill casting, as set forth below:

' Per cent Magnesium 7.0-8.5 Titanium 0.10-0.25 Manganese 0.20-0.60 Beryllium 0.001-0.07 Boron 0.001-0.01 Aluminum plus impurities balance In either of these more specific formulations, chromium, 0.15-0.50 percent, may be substituted for the manganese component. For best results by either method of casting, the total impurities, which include metals of the type copper, iron, and silicon, should be kept below 0.45 percent with 0.25 percent being the maximum for any of the named metallic impurities. Since alkali metal, alkaline earth metals, and, especially, metallic sodium are very deleterious to the physical properties of the alloy, inclusion of more than 0.001 percent should be avoided.

Thefollowing formulations are given by way of illustration but not by way of limitation of compositions which give excellent properties'for both sand and chill astmgar'is superior pro erties in chill casting:

Ewample Per cent Magnesium 7.0 Titanium 1 0.20 Manganese -e 0.25 Beryllium 0.010 Boron 0.003 Aluminum plus impurities balance Ea'ample 2 Percent Magnesium 7.5 Titanium 0.20 Manganese 0.30 Beryllium 0.055 Boron 0.003 Aluminum plus impurities balance Example 3 Per cent Magnesium 6.5 Titanium 0.20 Maganese 0.20 Beryllium 0.050 Boron 0.003 Aluminum plus impurities balance Example 4 Per cent Magnesium 6.5 Titanium 0.20 Manganese Beryllium 0.010 Boron 0.003 Aluminum plus impurities balance It will be apparent from this description that I have conceived of heretofore unknown alloying principles which have led to the inclusion of various alloying elements to produce aluminummagnesium alloys having characteristics far superior to those presently known, as produced by sand casting or chill casting with or without heat treatment. or considerable importance is the possibility of using the resulting compositions interchangeably for casting in permanent molds or green sand without deleteriously affecting the physical properties.

Evident also is the fact that for the first time in aluminum-magnesium alloys, elements may be incorporated for the purpose of increasing yield strength to a desirable high value without the lowering of ultimate strength and elongation. These and other concepts have led to the production of aluminum-magnesium alloys having considerable advantage over those heretofore produced.

It will be understood that numerous changes may be made in the amounts of materials and methods of incorporation and fabrication into a cast product without departing from the spirit of my invention, especially as defined in the following claims.

I claim as my invention:

1. An aluminum base casting alloy consisting essentially of from 1 to 9 percent by weight magnesium, from 0.001 to less than 0.01 percent by weight boron, from 0.001 to 0.4 percent by Weight titanium, from 0.001 to 0.2 percent by weight beryllium, from 0.15 to 1.5 percent by weight manganese, and less than 0.45 percent by weight impurities, the balance being aluminum.

2. An aluminum base casting alloy consisting essentially of from 1.to 9 percent weight mg 1 nesium, from 0.001 to less than 0.01 percent by weight boron, from 0.001 to 0.4 percent by weight titanium, from 0.001 to' 0.2 percent by weight beryllium, from. 0.15 to 1.5fpercent by weight manganese, and less than 0.45 percent by weight impurities including a maximum of 0.25 percent by weight of any of the metals selected from the group consisting of-copper, silicon and iron, the balance being aluminum.

3. An aluminum base castingallo consisting essentially of from 1 to 9 percent by weight magnesium, from0.001 to less than 0.01 percent byweight boron, from 0.001 to 0.4 percent by weight titanium, from'0.00l to 0.2 percent by weight beryllium, from 0.15 to 1.5 percent by weight manganese, and less than 0.45 percent by weight impurities including less than 0.001 percent by weight of an alkali metal, the balance being aluminum.

4. An aluminum base casting alloy consisting essentially of from 1 to 9 percent by weight magnesium, from 0.001 to less than 0.01 percent by weight boron, from 0.001 to 0.4 percent by weight titanium, from 0.001 to 0.2 percent by weight beryllium, from 0.15 to 1.5 percent by weight manganese, and less than 0.45 percent by weight impurities including a maximum of 0.001 percent by weight of any alkaline earth metal, the balance being aluminum.

5. An aluminum base casting alloy consisting essentially of from 3 to 9 percent by weight magnesium, from 0.001 to less than 0.01 percent by weight boron, :from 0.01 to 0.25 percent by weight r titanium, from 0.001 to 0.07 percent by weight beryllium, from 0.2 to 0.06 percent by weight manganese, and less than 0.45 percent by weight impurities, the balance being aluminum.

6. An aluminum base casting alloy consisting essentially of from 3 to 9 percent by weight ma nesium, from 0.001 to less than 0.01 percent by weight boron, from 0.01 to 0.25 percent by weight titanium, from 0.001 to 0.03 percent by weight beryllium, from 0.15 to 0.3 percent by weight manganese, and less than 0.45 per cent by weight impurities, the balance being aluminum.

7. An aluminum base casting allo-y consisting essentially of 3 to 9 percent by weight magnesium, from 0.001 to less than 0.01 percent by weight boron, from 0.01 to 0.25 percent by weight titanium, from 0.001 to 0.2 percent by weight beryllium, from 0.15 to 1.5 percent by weight manganese, and less than 0.45 percent by weight impurities including a maximum of 0.25 percent by weight of any of the metals selected from the group consisting of copper, silicon and iron, and a maximum of 0.001 percent by weight of any of the metals selected from the group consisting of alkali metals and alkaline earth metals, the balance being aluminum.

8. An aluminum base casting alloy for sand casting consisting essentially of 6 to 7.5 percent by weight magnesium, 0.001 to less than 0.01 percent by weight boron, 0.1 to 0.25 percent by weight titanium, from 0.001 to 0.03 percent by weight beryllium, 0.15 to 0.3 percent by weight manganese, and less than 0.45 percent by weight impurities including metals selected from the group consisting of copper, silicon and iron, the balance being aluminum.

9. An aluminum base casting alloy for chill casting consisting essentially of from 7 to 8.5 percent by weight magnesium, from 0.001 to less than 0.01 percent by weight boron, 0.1 to 0.25 percent by weight titanium, 0.001 to 0.07 percent 11 by weight, beryllium, 0.2 to 0.6 percent by weight manganese, and less than 0.45 percent by weight impurities including metals selected from the group consisting of copper, silicon and iron, the balance being aluminum.

CHARLES B. WILLMORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Number Country Date 467,672 Great Britain June 16, 1937 523,120 Great Britain July 5, 1940 OTHER REFERENCES Practical Metallurgyl by Sachs and. Van Horn,

published by the American Society for Metals. 1940, page32.

Metal Industry July 25, 1947, page 71.

Material and Methods, January 1947, pages 68-71.

Foundry Trade Journal," November 17, 1938. pages 373 and 374. 

7. AN ALUMINUM BASE CASTING ALLOY CONSISTING ESSENTIALLY OF 3 TO 9 PERCENT BY WEIGHT MAGNESIUM, FROM 0.001 TO LESS THAN 0.01 PERCENT BY WEIGHT BORON, FROM 0.01 TO 0.25 PERCENT BY WEIGHT TITANIUM, FROM 0.001 TO 0.2 PERCENT BY WEIGHT BERYLLIU, FROM 0.15 TO 1.5 PERCENT BY WEIGHT MANGANESE, AND LESS THAN 0.45 PERCENT BY WEIGHT IMPURITIES INCLUDING A MAXIMUM OF 0.25 PERCENT BY WEIGHT OF ANY OF THE METALS SELECTED FROM THE GROUP CONSISTING OF COPPER, SILICON AND IRON, AND A MAXIMUM OF 0.001 PERCENT BY WEIGHT OF ANY OF THE METALS SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS, THE BALANCE BEING ALUMINUM. 